We set a maintenance period, then performed the maintenance. All but one item went back to OK. When the maintenance period ended, the one item still in PROBLEM status caused a notification to be sent. All was as expected.

The ONLY odd thing is that on the Dashboard, the Actions column for this item showed a "-" instead of a "1".

The Item, Trigger, Maintenance, and Action all work correctly. The only bug is the display issue in the Dashboard.